[jira] [Commented] (CALCITE-6645) Support user-defined function without parentheses when db dialect's allowNiladicParentheses property is false

["hongyu guo (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-6645?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17907313#comment-17907313 ] 

hongyu guo commented on CALCITE-6645:
-------------------------------------

This PR has changed the default behavior of calcite. The default SqlConformance does not allow Niladic Parenthethes, so the syntax of UDF will be `Syntax.FUNCTION_ID`。 Before this PR, it is `Syntax.FUNCTION`。 Our program will encounter errors after upgrading to the current version

[~duanzhengqiang] [~mbudiu] 

> Support user-defined function without parentheses when db dialect's allowNiladicParentheses property is false
> -------------------------------------------------------------------------------------------------------------
>
>                 Key: CALCITE-6645
>                 URL: https://issues.apache.org/jira/browse/CALCITE-6645
>             Project: Calcite
>          Issue Type: Improvement
>    Affects Versions: 1.38.0
>            Reporter: Zhengqiang Duan
>            Assignee: Zhengqiang Duan
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.39.0
>
>
> Hi community, When I implement a user defined function without parameters for Oracle database, I get a `Column 'SYS_DATE' not found in any table` exception when I execute the `SELECT SYS_DATE FROM DUAL` statement. I did some research and found that the default SqlSyntax used by the SqlUserDefinedFunction is SqlSyntax.FUNCTION, and its corresponding function syntax is SYS_DATE() instead of SYS_DATE. SqlSyntax.FUNCTION will cause an exception during SQL validation. The implementation logic of makeNullaryCall in SqlValidatorImpl is as follows, since makeNullaryCall checks if operator.getSyntax() == SqlSyntax.FUNCTION_ID, user defined function cannot be converted to SqlBasicCall.
> {code:java}
> @Override
> public @Nullable SqlCall makeNullaryCall(SqlIdentifier id) {
>     if (id.names.size() == 1 && !id.isComponentQuoted(0)) {
>         final List<SqlOperator> list = new ArrayList<>();
>         opTab.lookupOperatorOverloads(id, null, SqlSyntax.FUNCTION, list, catalogReader.nameMatcher());
>         for (SqlOperator operator : list) {
>             if (operator.getSyntax() == SqlSyntax.FUNCTION_ID) {
>                 // Even though this looks like an identifier, it is a
>                 // actually a call to a function. Construct a fake
>                 // call to this function, so we can use the regular
>                 // operator validation.
>                 return new SqlBasicCall(operator, ImmutableList.of(), id.getParserPosition(), null).withExpanded(true);
>             }
>         }
>     }
>     return null;
> }{code}
> In order to support user defined functions without parameters, we need to modify the logic of the CalciteCatalogReader#toOp method. If the current user defined function has no parameters and allowNiladicParentheses is set to false, SqlSyntax.FUNCTION_ID should be passed in for SqlUserDefinedFunction.
> {code:java}
> SqlSyntax syntax = function.getParameters().isEmpty()
>     && !config.conformance().allowNiladicParentheses()
>     ? SqlSyntax.FUNCTION_ID
>     : SqlSyntax.FUNCTION;
> return new SqlUserDefinedFunction(name, kind, returnTypeInference,
>     operandTypeInference, operandMetadata, function, syntax);{code}
> I will submit a PR to support this usage. if anyone can provide some suggestions I would appreciate it.



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